Biodegradable nano-polymer compositions and biodegradable articles made thereof

ABSTRACT

The invention relates to biodegradable nano-polymer compositions, or nanocomposites, comprising poly(lactic acid) and co-polyester polymer with adipic acid compounded with nanoparticles of a mineral material having a degree of purity of at least 99.9%, preferably 99.99%, selected from the group of silica and magnesium silicate. In addition, the present invention refers to a process for manufacturing the said compositions as well as biodegradable articles made on the basis of such compositions, such as molded, formed and extruded articles.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/365,579, filed Feb. 28, 2006, which is incorporated herein byreference in its entirety.

FIELD

The present invention relates to biodegradable polymer nanocompositescomprising poly(lactic acid) compounded with nanoparticles of anextremely pure mineral, silica based material. The invention furtherrefers to a process for manufacturing said nanocomposites or, in otherwords biodegradable nano-polymer compositions, and to biodegradablearticles made on the basis of said compositions as well.

BACKGROUND

Packaging material and disposable beakers, cups and cutlery are usednowadays widely and allow that food material may be sold and/or consumedunder hygienic conditions. Such disposable materials and objects arehighly estimated by the consumers and the retailers, since they may besimply disposed after use and do not have to be washed and cleaned likeconventional dishes, glasses or cutlery.

Yet, the widespread and even growing use of such materials result in amounting amount of litter produced each day. Currently, the plasticwaste is either provided to garbage incinerators or accumulates inrefuse dumps, with both of the above-mentioned solutions for wastedisposal being associated with problems for the environment.

Thus, there is a need in the art to obviate the above problem and toprovide materials, which combine the advantages of currently usedplastics material and do not add to environmental pollution.

For preparing the above mentioned items several biodegradable polymersare already known in the state of the art and comprise materials on thebasis of e.g. poly(glycolic acid), poly(epsilon-caprolactone),poly(lactic acid), and polydioxanone. The production of these polymersis, however, rather cumbersome and expensive, so that the use thereof ispresently mainly restricted to high value medical applications requiringbioabsorbable materials. A few biodegradable resins have been used inapplications such as described above but cost has made themun-affordable by the consumers.

An object of the present invention is thus to provide a biodegradablearticles or items comprising a polymer composition, which composition isdegraded in a natural environment in a time period which issignificantly shorter as compared to the time period required for thedegradation of conventional plastic materials, such as e.g.polyethylene. In a controlled environment such as a composting site thecomposition will allow biodegradation in period of time not to exceed180 days, one of the time requirements set by the US specification setby ASTM (ASTM 6400 D99). Moreover, such a composition should also enableproduction of bags, bottles or cutlery, exhibiting desired propertiesfor the respective purpose.

Another object of the invention is to provide biodegradable compositionswhich exhibit increased mechanical and/or thermal performance ascompared to the current ones, e.g. thermal stability or thermalresistance, improved processability or flexibility.

Nanocomposites are rapidly expanding new plastic technology, offeringpromise for enabling novel polymer material. It appears that the “nanoeffect” allows certain polymers or polymer compositions such as biobasedor biodegradable polymer compositions to bridge the gap with the use ofconventional petroleum based plastics, allowing such novel material toachieve physical properties that open the uses of these novel materialsin significantly broader technical or commercial applications.

The incorporation into such plastics of nano-sized fillers, whether theyare minerals or organic fibers, creates foundation of polymernanocomposites. The benefits of nanocomposites extend well beyond one ortwo improvements but translate into several improvements of physical andthermal properties of polymers at such degree that the starting corepolymer matrix composition is modified into new shapes or structures,which allow eventually the creation of completely novel material orfeatures.

The physical and thermal properties of the new polymer nanocompositesare so altered as compared to standard polymer material that theinventor retains that there is creation of a brand new material to becalled “biodegradable nano-polymer composition”.

These and other objects which will become apparent from the subsequentdetailed description of the present invention, which provides amongothers a composition comprising between about 40 and 97% by weight ofpoly(lactic acid) polymer, between about 0.5 and 35% by weight ofco-polyester polymer with adipic acid, and up to about 6% ofnanoparticles of an extremely pure mineral material, in particular amineral material having a degree of purity of at least 99.9%, selectedfrom the group of silica and magnesium silicate, each on the basis ofthe total weight of the biodegradable polymer composition.

SUMMARY

A composition of the present invention is biodegradable when exposed tospecific environmental conditions, such as composting, which will resultin a loss of some properties that may be measured by standard methodsappropriate to the plastic and in the application in a period of timethat determines its classification. For instance composting is a managedprocess that controls the biological decomposition and transformation ofbiodegradable materials into humus-like substance called compost: theaerobic mesophilic and thermophilic degradation of organic matter tomake compost; the transformation of biologically decomposable materialthrough a controlled process of biooxidation that proceed throughmesophilic and thermophilic phases and results in the production ofcarbon dioxide, water, minerals, and stabilized organic matter (compostor humus) (ASTM Terminology) Consequently all main components,poly(lactic acid) and co-polyester polymer with adipic acid will bedegraded to small organic fragments which will create stabilized organicmatter and will not introduce any hazard or heavy metals into soil.

As a result, objects made from the composition of the present inventionwill not contribute to a further increase of refuse dumps; on thecontrary will allow creation of organic fertilizers such as compost,while such objects simultaneously provide all advantages of disposableobjects highly estimated by the consumers and producer. Objects made ofa composition according to the present invention may be disposed afteruse, are essentially of lightweight, and have not to be transported to alocation where they have to be cleaned. In particular, objects made froma composition according to the present invention provide the advantagethat objects thrown away in parks or at the beach will degrade and willvanish after some time. However this invention should not be publicizeas a license to litter the environment.

Moreover, a composition according to the present invention may beproduced completely or partially from renewable sources, when desired.In addition, a composition according to the present invention may beadapted to various processing methods known in the art.

Biodegradable polymers such as polylactides (PLAs) have been producedfor many years. PLA resemble clear polystyrene and have good gloss andclarity for aesthetic appeal, along with physical properties well suitedfor use as fibers, films, and thermoformed packaging. PLA is alsobiocompatible and have been used extensively in medical and surgicalapplications, i.e. sutures and drug delivery devices. Unfortunately, PLApresent major weaknesses such as brittleness as well as low thermalresistance, 136° F. (58° Celsius) and moisture-related degradation,limiting a lot of commercial applications.

Unexpectedly, the compositions according to the present inventionprovide physical properties which are not inherent to poly(lactic acid)and provide significant improvements with respect to the processability,production costs or heat resistance along with improved flexibility andductility without decreasing their biodegradability.

It is assumed that the combination of a blending step performed atambient temperature followed by extrusion at relatively high temperatureand pressure through e.g. a twin screw extruder allow the creation of abrand new shape, structure or morphology of the polymer. Extrusion ofthe blended polymer mass compounded with the selected mineralnanoparticles at a high temperature induces shear forces which promotean exfoliation and dispersion of the components: as a result of it, thenew polymer composition is constructed by evenly dispersing the selectedmineral material into nanoparticles that form platelets.

The dispersion of the platelets is critical to make the compositionsimproved and the inventor has especially worked on avoiding the creationof aggregate of platelets, which would prevent the improvement in theproperties herein described.

Such a performance has been achieved according to the present inventionby making use for mixing the mineral nanoparticles of a custom designedside feeder, e.g. a tower to enter the barrel of the extruder; whiledoing so the inventor avoid direct injection of the nanoparticles to themolten polymer material and so allows the necessary good and smoothdistribution of the said platelets during mixing and extrusion. As aresult of it, these platelets are evenly distributed throughout thepolymer matrix to create multiple parallel layers typical of the newpolymer morphology mentioned here above.

It has been further noted that not only the size, namely the averagesize of the nanoparticles is important, but that the degree of purity ofthe selected mineral material is crucial to achieve the desired newfeatures: a degree of purity of at least 99.9%, preferably of at least99.99% is necessary for that.

The new shape, structure or morphology which characterizes thenano-polymer composition of the invention is tremendously andsurprisingly improving the physical properties of the composition,namely its thermal properties and thermal stability: e.g., suchcompositions exhibit a significant improvement in terms of thermalresistance, of the magnitude of 35 to 45° F. (about 1.7 to 7.2° C.)depending on specific formulations.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description.

DETAILED DESCRIPTION

The present invention relates to a biodegradable plastic. The term“biodegradable plastic” pertains to a degradable plastic in which thedegradation results from the action of naturally occurringmicroorganisms such as bacteria, fungi, and algae. A degradable plasticis a plastic designed to undergo a significant change in its chemicalstructure under specific environmental conditions, resulting in a lossof some properties that may be measured by standard tests methodsappropriate to the plastic and the application in a period of time thatdetermines its classification. Depending on the additional componentspresent in the composition and the dimensions of the object made fromsaid biodegradable material, the time period required for degradationwill vary and may also be controlled when desired. Generally, the timespan for biodegradation will be significantly shorter than the time spanrequired for a degradation of objects made from conventional plasticmaterials having the same dimensions, such as e.g. polyethylene, whichhave been designed to last for as long as possible. For example,cellulose and Kraft paper is to biodegrade within 83 days in a compostenvironment. Our formulation is to biodegrade in a shorter period oftime and will pass the tests required by ASTM 6400 D99, which demandthat compostable plastic would biodegrade within less than 180 days.Articles made from PE would not degrade under normal compostingconditions and PLA-based article would degrade in compost environment inweeks (about 6 to 8 weeks).

Biodegradable polymers are comprised of components which are reduced infilm or fiber strength by microbial catalyzed degradation. Thebiodegradable polymers are reduced to monomers or short chains, whichare then assimilated by the microbes. In an aerobic environment, thesemonomers or short chains are ultimately oxidized to CO₂, H₂O, and newcell biomass. In an anaerobic environment the monomers or short chainsare ultimately oxidized to CO₂, H₂O, acetate, methane, and cell biomass.Successful biodegradation requires direct physical contact between thebiodegradable polymers and the active microbial population or theenzymes produced by the active microbial population. Moreover, certainminimal physical and chemical requirements such as suitable pH,temperature, oxygen concentration, proper nutrients, and moisture levelmust be met. (cf. U.S. Pat. No. 6,020,393)

A biodegradable composition according to the present invention comprisesbetween about 40% by weight to 97% by weight of poly(lactic acid)polymer, between about 0.5% by weight to 35% by weight of co-polyesterpolymer with adipic acid, and up to about 6% of nanoparticles of anextremely pure mineral material selected from the group of silica andmagnesium silicate, each on the basis of the total weight of thebiodegradable composition.

A composition according to the present invention may be obtained bymixing or blending the respective constituents in the desired amounts.This may be performed according to any method known in by the skilledartisan. For example, poly(lactic acid) polymer and co-polyester polymerwith adipic acid may be mixed in pure form, for example blended by meansof mill roll blending, and heated to a temperature chosen according tothe general knowledge in the art such that at least one of theabove-mentioned components is partially or essentially completelymolten.

Poly(lactic acid) may be represented by the following structure:

wherein n for example can be an integer between 10 and 250. Poly(lacticacid) can be prepared according to any method known in the state of theart. For example, poly(lactic acid) can be prepared from lactic acidand/or from one or more of D-lactide (i.e. a dilactone, or a cyclicdimer of D-lactic acid), L-lactide (i.e. a dilactone, or a cyclic dimerof L-lactic acid), meso D,L-lactide (i.e. a cyclic dimer of D-, andL-lactic acid), and racemic D,L-lactide (racemic D,L-lactide comprises a1/1 mixture of D-, and L-lactide).

The preparation of polyesters and copolyesters is well known in the art,such as disclosed in U.S. Pat. No. 2,012,267. Such reactions aretypically operated at temperatures from 150° C. to 300° C. in thepresence of polycondensation catalysts such as titanium isopropoxide,manganese diacetate, antimony oxide, dibutyl tin diacetate, zincchloride, or combinations thereof. The catalysts are typically employedin amounts between 10 to 1000 parts per million (ppm), based on totalweight of the reactants (cf. U.S. Pat. No. 6,020,393).

In addition to the Poly(lactic acid) and the copolyester of adipic acid,the composition is compounded with nanoparticles of a mineral materialselected from the group of silica and magnesium silicate. Nanoparticlesaccording to the invention define particles having a size definitelylower than the common size of current ground mineral equivalents whichare usually of the order of several microns; according to the presentinvention the nanoparticles have a size comprised between about 20 and amaximum of 500 nanometers; good performance can be achieved with amineral material the nanoparticles of which have an average particlesize of the order of 200 to 400, e.g. of about 250 nanometers.

Although size particle is a critical parameter to achieve the desiredperformance, the extremely high degree of purity of the mineral selectedtherefore is crucial. Best results are achieved by using nanoparticlesof at least 99.9%, preferably 99.99% pure silica or magnesium silicate.Special qualities of finely ground silica as provided by the specializedtrade have been proved suitable within the frame of the presentinvention.

The biodegradable polymer can further comprise between 1 and 32% byweight of mineral particles, each on the basis of the total weight ofthe biodegradable composition, said mineral particles comprising atleast one of magnesium and silicate. Examples for such minerals are e.g.montmorillonite or talc. The mineral act as filler adds strength andimparts stiffness. Usually, the mineral particles have a size of 0.2 to4.0 microns, more frequently a size of 1 to 2 microns.

Moreover, during the preparation of a biodegradable polymer according tothe present invention organic peroxide may be added to the reactionmixture in an amount of less than 5% by weight, on the basis of thetotal weight of the biodegradable final polymer composition.

Examples for organic peroxides which may be used for preparing acomposition according to the present invention are e.g. diacetylperoxide, cumyl-hydroperoxide, and dibenzoyl peroxide. Other organicperoxides known to a skilled person may be used as well. The organicperoxides serve as radical starter molecules initiating a polymerizationand help to provide connections, in particular covalent bonds, betweenthe components present in a composition according to the presentinvention.

Depending on the specific applications desired, a biodegradable polymercomposition of the present invention may also comprise additionaladditives or components well known in the art, namely biodegradablecomponents or additives such as e.g. natural coloring agents, additionalpolymeric compounds like starch, processed starch, cellulose, cellulosefibers, proteins, protein fibers, etc.

A composition of the present invention may be used for the production ofvarious articles, such as e.g. molded articles and/or extruded articles.The term “molded article” (or “extruded article”) as used in the presentinvention comprises articles made according to a molding process (or anextrusion process). A “molded article” (or “extruded article”) can alsobe part of another object, such as e.g. an insert in a container or aknife blade or fork insert in a corresponding handle.

The figures here below are provided for exemplification only and theycan be modified by the skilled artisan to the necessary extent,depending on the special features which are looked for.

A molded article according to the present invention comprises abiodegradable composition, which biodegradable composition comprisesbetween 40 and 97%, e.g. about 91% by weight of poly(lactic acid)polymer, and between 0.5 and 35%, e.g. 5% by weight of co-polyesterpolymer with adipic acid, and about 4% of at least 99.9%, preferably99.99% pure finely ground silica, each on the basis of the total weightof the biodegradable composition.

According to another embodiment of the invention the molded articlecomprises a biodegradable composition, which biodegradable compositioncomprises e.g. about 75% by weight of poly(lactic acid) polymer, e.g. 5%by weight of co-polyester polymer with adipic acid, e.g. about 15% ofmineral particles of magnesium silicate or talc, and about 5% of atleast 99.9%, preferably 99.99% pure finely ground silica, each on thebasis of the total weight of the biodegradable composition. Examples forvarious molded article are utensils, forks, spoons, knives, chopsticks,containers and cups.

An extruded article according to the present invention comprises abiodegradable composition, which biodegradable composition comprisesbetween 40 and 97% by weight of poly(lactic acid) polymer, and between0.5 and 35% by weight of co-polyester polymer with adipic acid, each onthe basis of the total weight of the biodegradable composition. Inparticular, a biodegradable composition for an extruded articleaccording to the present invention can comprise between 50 and 85%, e.g.75% by weight of poly(lactic acid) polymer, between 2 and 20%, e.g. 15%by weight of co-polyester polymer with adipic acid and about 5% of atleast 99.9%, preferably 99.99% pure finely ground silica, each on thebasis of the total weight of the biodegradable composition. Extrudedarticles may be for example films, trash bags, grocery bags, containersealing films, pipes, drinking straws, spun-bonded non-woven materials,and sheets.

A formulation for a profile extrusion process on the basis of acomposition according to the present invention can comprise e.g. 75% byweight of poly(lactic acid) polymer, about 15% by weight of co-polyesterpolymer with adipic acid, and about 5% of at least 99.9%, preferably99.99% pure finely ground silica, each on the basis of the total weightof the biodegradable composition. Articles according to the presentinvention made from a profile extrusion formulation are for exampledrinking straws and pipes.

A formulation for a thermoform extrusion process on the basis of acomposition according to the present invention can comprise between 75%and 85% by weight of poly(lactic acid) polymer, between 5% and 15% byweight of co-polyester polymer with adipic acid, between 5% and 15% byweight of mineral particles comprising at least one element selectedfrom the group consisting of magnesium and silicate, preferably about75% by weight of poly(lactic acid) polymer, about 15% by weight ofco-polyester polymer with adipic acid, about 9% by weight of magnesiumsilicate or talc, and about 5% of at least 99.9%, preferably 99.99% purefinely ground silica.

Articles according to the present invention made from a thermoformextrusion method are e.g. sheets for producing cups, plates and otherobjects, which could be outside of the food service industry.

As outlined in detail before, the composition for the preparation ofsuch molded articles can comprise in addition to the above-mentionedcomponents organic peroxide(s), mono ester(s), and/or naturalplasticizer(s).

Injection molding, profile extrusion and thermoform extrusion areprocesses known to a skilled person and are described for example inModern Plastics Encyclopedia, Published by McGraw-Hill, Inc.—mid-October 1991 edition.

The present invention will be described now in detail on the basis ofthe following non-limiting examples given by way of an example only.

Example 1

Injection Molding Formulations

Several injection molding formulations have been using the followingingredients in proportions varying within the ranges provided herebelow:

from 75% to 91% by weight poly(lactic acid) polymer

from 2% to 5% by weight (co-polyester polymer with adipic acid)

from 0.2% to 4% by weight of finely ground 99.99% pure silica**.

(** average size particle of about 250 nanometers)

It is crucial that introducing the mineral nanoparticles be performedwithout creating aggregates, using for instance a side-feeder that wouldnot inject the nanoparticles directly into the barrel of the extruderbut through a tower letting the nanoparticles fall and mix smoothly withthe molten material.

The above-mentioned compounds are mixed by means of extrusioncompounding at a temperature not to exceed 160° C. over a period rangingfrom 25 sec to 2 min. Then, the resulting mixture is filled in aninjection molding device at a temperature of about 160° C. and isinjected into a mold at a temperature of about 20° C. in order to obtainan injection molded cup.

Example 2

Injection Molding Formulation (Specific)

An injection molding formulation is prepared which comprises:

74.5% by weight poly (lactic acid) polymer

5% by weight (co-polyester polymer with adipic acid)

15% by weight of magnesium silicate (talc)

5% by weight of finely ground 99.99% pure silica**, and

0.5% by weight of 2,5-Dimethyl-2,5-di(t-butyl peroxy) hexane.

(** average size particle of about 250 nanometers)

The injection molding formulation is prepared as detailed in Example 1and injection molded products may be obtained according to the stepslined out in said Example 1.

The above formulations are provided for exemplification only and theycan be modified by the skilled artisan to the necessary extent,depending on the special features which are looked for.

Example 3

Profile Extrusion Formulation

Several profile extrusion formulations have been using the followingingredients in proportions varying within the ranges provided herebelow:

from 65% to 75% by weight poly lactic acid polymer

from 15% to 20% by weight of co-polyester polymer with adipic acid, and

from 1% to 5% by weight finely ground 9.99% pure silica**.

(**average size particle of about 250 nanometers)

The above-mentioned compounds are mixed by twin screw compounding. Theresulting mixture is filled in a profile extrusion device at atemperature not to exceed 160° C. and a tube is obtained which may beused as a drinking straw.

The above formulations are provided for exemplification only and theycan be modified by the skilled artisan to the necessary extent,depending on the special features which are looked for.

Example 4

Thermoform Extrusion Formulation

Several thermo form extrusion formulations have been using the followingingredients in proportions varying within the ranges provided herebelow:

from 55% to 75% by weight poly lactic acid polymer

from 5% to 15% by weight of co-polyester polymer with adipic acid

from 4% to 9% by weight of magnesium silicate (talc)

from 1% to 5% by weight finely ground 99.99% pure silica**, and

from 0.2% to 1% by weight of 2,5-Dimethyl-2,5-di(t-butyl peroxy) hexane.

(**average size particle of about 250 nanometers)

The above-mentioned compounds are mixed by twin screw compounding. Theresulting mixture is filled in a thermoform extrusion device at atemperature not to exceed 160° C. and a sheet having a thickness between0.1 mm to 45 mm is obtained which may be used for forming cups, platesor bottles.

The above formulations are provided for exemplification only and theycan be modified by the skilled artisan to the necessary extent,depending on the special features which are looked for.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A biodegradable composition, comprising: between 40 and 97% by weight of poly(lactic acid) polymer (PLA); between 0.5 and 35% by weight of a co-polyester polymer with adipic acid; and more than 0% and up to 6% by weight of nanoparticles of an extremely pure mineral material selected from the group consisting of silica and magnesium silicate, each on the basis of the total weight of the biodegradable polymer composition.
 2. The biodegradable polymer composition according to claim 1, wherein the nanoparticles of mineral material have a size comprised between about 20 and 500 nanometers.
 3. The biodegradable polymer composition according to claim 1, wherein the nanoparticles of mineral material have a degree of purity of at least 99.9%.
 4. The biodegradable polymer composition according to claim 1, comprising between 1 and 32% of particles of mineral filler comprising magnesium silicate or talc having a particle size comprised between about 0.2 and 4.0 microns.
 5. The biodegradable polymer composition according to claim 1, to which composition during its preparation more than 0% and less than 5% of an organic peroxide, on the basis of the total weight of the final biodegradable composition, has been added.
 6. The biodegradable polymer composition according to claim 3, wherein said organic peroxide is selected from the group consisting of diacetyl peroxide, cumyl-hydro-peroxide, and dibenzoyl peroxide, dialkyl peroxide, 2,5-methyl-2,5-di(terbutylperoxy)-hexane and mixtures thereof.
 7. A molded, extruded or thermoformed article comprising a biodegradable composition, said biodegradable composition comprising: between 40 and 97% by weight of poly(lactic acid) polymer; between 0.5 and 35% by weight of co-polyester polymer with adipic acid; and more than 0% and up to 6% by weight of nanoparticles of an extremely pure mineral material selected from the group consisting of silica and magnesium silicate, each on the basis of the total weight of the biodegradable polymer composition.
 8. The article according to claim 7, wherein the nanoparticles of mineral material have a size comprised between about 20 and about 500 nanometers.
 9. The article according to claim 7, wherein the nanoparticles of mineral material have a degree of purity of at least 99.9%.
 10. The article according to claim 7, said article being selected from the group consisting of utensils, food service-ware, forks, spoons, knives, chopsticks, containers, cups, plates and pots.
 11. The article according to claim 7, which further comprises particles of mineral filler comprising magnesium silicate or talc having the particle size comprised between about 0.2 and about 4.0 microns.
 12. The article according to claim 7, to which composition during its preparation more than 0% and less than 5%, of organic peroxide, on the basis of the total weight of the biodegradable composition, has been added.
 13. A method of producing an article comprising a biodegradable composition, said process comprising the steps of: (i) providing a biodegradable composition, said composition comprising between 40 and 97% by weight of poly(lactic acid) polymer, and between 0.5 and 35% by weight of co-polyester polymer with adipic acid, each on the basis of the total weight of the biodegradable composition, and more than 0% and up to 6% by weight of nanoparticles of an extremely pure mineral material selected from the group consisting of silica and magnesium silicate; (ii) mixing the constituents of (i) so as to prevent the creation of aggregates; (iii) heating the mixture to a temperature of from 95 to 135° C.; and (iv) forming the resultant mixture to obtain a desired shape.
 14. The method according to claim 13, wherein the mineral nanoparticles are directly introduced into the barrel of the mixer/extruder.
 15. The method according to claim 14, wherein the mineral nanoparticles are introduced into the barrel of the mixer/extruder through a side feeder.
 16. The method according to claim 13, wherein the nanoparticles of mineral material have a size comprised between about 20 and about 500 nanometers.
 17. The method according to claim 13, wherein the nanoparticles of mineral material have a degree of purity of at least 99.9%.
 18. The method according to claim 13, which comprises adding to the biodegradable composition provided according to step i) between 1% and 32% of particles of mineral filler comprising magnesium silicate or talc having a particle size comprised between about 0.2 and about 4.0 microns.
 19. The method according to claim 13, which comprises adding to the biodegradable composition provided according to step i) more than 0% and less than 5% of organic peroxide.
 20. The method according to claim 13, wherein the step of forming includes subjecting said biodegradable composition to a process selected from the group consisting of injection molding, profile extrusion, and thermoform extrusion.
 21. The biodegradable polymer composition according to claim 3, wherein the degree of purity is 99.99%.
 22. The article according to claim 9, wherein the degree of purity is 99.99%.
 23. The method according to claim 17, wherein the degree of purity is 99.99%. 